1. Field of the Invention
The present invention relates to a light emitting device having auto-cloning photonic crystal structures, and more particularly to a light emitting device having auto-cloning photonic crystal structures marked by higher light extraction efficiency.
2. Description of the Prior Art
Solid-state light-emitting devices have advantages of longer life time, shorter response time, compact dimensions and lower driving voltage, etc. Especially gallium nitride light emitting devices become mainstream of new light sources of next generation, because the energy band gap of gallium nitride is relatively wide enabling gallium nitride to emit light of short wavelength and emit white light by combining with fluorescence. A sapphire is commonly used as a substrate of a gallium nitride light emitting device of the prior art. Because the sapphire is substantially transparent for visible light, light generated by the light emitting device emit omnidirectionally and does not concentrate to output at one surface, resulting in lower luminescence efficiency at the surface. Therefore, there has been increasing demand for developing light emitting device with high luminescence efficiency.
A prior art manufacturing method of light emitting diodes improves luminescence efficiency by disposing a reflecting surface on a substrate of a light emitting diode for reflecting lights emitted toward the substrate. However, the light reflected by the reflecting surface is continuously reflected inside the light emitting diode, because total internal reflection has occurred. The reflected light is eventually absorbed by the material of the light emitting diode and converted to heat, which impedes the luminescence efficiency of the light emitting diode. Another prior art method for enhancing luminescence efficiency embeds a reflecting surface in a semiconductor layer of a light emitting diode for the reflecting surface to be closer to an active layer of the light emitting diode by using Epitaxial Lateral Over-Growth (ELOG). However, the reflecting surface must be etched to expose the semiconductor layer for the following manufacturing process of the light emitting diode by using ELOG. Thus, the area of the reflecting surface is decreased and the luminescence efficiency is impeded.